Treatment of chemical pulp



Patented Mar. .7, 1939 PATENT orrlcap TREATMENT or CHEMICAL PULP Frederick F. Frlck, Anaconda, Mont., assignor to International smelting and Refining Company, East .Chicago, In a corporation of Montana No Drawing.

Serial No. 72,770

7 Claims.

' This invention relates to the separation of solid matter from liquids by decantation, sedimentation, settlement, or the like, and has for an ob- Ject the provision ofan improved method of increasing the rate of settlement of solid matter from a chemical or metallurgical pulp. The invention constitutes an improvement of the process described and claimed in my copending application Serial No: 43,197, filed October 2, 1935, of

10 which the present application is a continuation in part.

In any process involving the separation of solids from a liquid by de'cantation, sedimentation, settlement, or the like, a mixture comprising a solid and liquid phase is introduced into a suitable container and is allowed to remain therein for a suflicient period of time to permit the relatively heavy solid particles to settle to the lower portion of the container. The supernatant" liquid 50 is then withdrawn from the upper portion of the container. The operation may, be conducted inv a continuous manner by continuously introducing the suspension-into the container'and continuously and separatelywithdrawing the suspended matter and the supernatant liquid, or batches of the liquid-solid mixture may be treated individually. In either case the speed and emciency with which the separation is eflected depend upon the rate at which the. solid particles 30 settle in the liquid medium in which they are suspended, Anymethod which will increase the rate at which settlement occurs will in general improve both the speed and efliciency of the separation. 35 The present invention p-0vldes an improved v method for increasing the rate of settlement of suspended matter in chemical or metallurgical pulps and thereby increasing the speed and efli- .ciency of decantation and similar operations. 40 The term, pulp as employed herein refers to a mixture of solid and liquid matter. The solid component of the pulp may comprise one or more substances and may range in particle size from extremely fine to rather coarse. The liquid com- 45 ponent, generally aqueous, may consist of a relatively pure liquid, or it may comprise a solution of two or more liquids or a solution of a normally solid substance in a liquid, for example, an aqueous salt solution. 50 -In my aforementioned application, I have described and claimed a method of increasing the rate of settlement of suspended matter in pulp 55 and incorporating the cooked emulsion in the Application April 4, 1936,

pulp. I have now discovered that the effectiveness of the cooked emulsion can be much improved by incorporating therein an alkaline reagent. I prefer to employ a caustic alkali metal compound such as caustic soda and to incorporate 'it in the emulsion by adding it to the starchbearing material during the cooking operation. When an alkaline agent such as caustic soda is used, the resulting product is clearer, thinner and more uniform, and it is considerably more efiective as .a coagulant than the cooked starch-bearing material alone.

In carrying out a preferred method of the invention, an emulsion comprising a starch-bearing material and caustic soda is prepared and incorporated in the pulp prior to carrying out the separation of the solid and liquid components thereof. Apparently, the starch, upon being incorporated in the pulp,.causes the particles of ably its action is mainly physical in nature.

Caustic soda is sometimes employed as a'dispersing agent for colloidal sols, and it is thought that when incorporated in the emulsion, the caustic soda serves to disperse the colloidal starch particles and thereby form a more uniform emulsion.

Any suitable starch-bearing material may be employed in preparing the emulsion. Starch itself may be used, or starch-bearing grains or vegetables may in some cases prove eifective.

Grain flour, however, has been found to be a particularly satisfactory starch-bearing material,

and its use generally is preferred. Particular reference will therefore be made to starch-bearing emulsions prepared from flour. For purposes of economy in practicing the invention, relatively low-grade flour products such, for example, as. foundry flour may be employed advantageously.

l-ligh grade caustic soda '(sodium hydroxide),

although it may be used, is not necessary in preparing the emulsion; ordinary cmmercial caustic soda will serve very well. In general, a fcooked aqueous emulsion is preferred in carrying out the method of the invention. Such an emulsion may be prepared by mixing the starch-bearing material, for example, flour, and water in suitable proportions, say one pound of flour to ten gallons of water, and heating (cooking) the mixture, preferably at the boiling point for about five to ten minutes. The heating may be accomplished by heating the container in which the water-flour mixture is prepared, or live steam may be introduced directly into the mixture. is added to the flour-water mixture during the cooking operation in an amount correspondingto one part by weight of caustic soda to about five to twenty parts by weight of flour; in other words, for each pound of flour in the mixture, about 0.2 1 to about 0.05 pound of caustic soda is added. The resulting cooked emulsion is added to the pulp prior to decantation or' other similar operation and preferably is incorporated therein by agitation.

As a specific example of the method of the present invention, its use in conjunction with the process described and claimed in the copending application of Frederick F. Frick and Jehu P. Cooper, Serial Number 751,448, filed November 5, 20 1934, is described below. In the process of that application, slime products containing tin, lead, antimony, and the like, obtained during the processing of secondary metals for the recovery of metal values, are treated for separation of their 25 lead content, which is in the form of lead sulphate. The slime is first treated with a water solution of an alkali metal carbonate, which converts the lead to lead carbonate. The insoluble lead carbonate, together with insolublertin-bear- 30 ing material, is separated from the resulting alkali metal sulphate solution by decantation, and the residue is washed by repeated agitation with water, followed by further decantation. The washed residue of lead carbonate and tin- 35 bearing materialv is treated with nitric acid to dissolve the lead carbonate, leaving the tin compounds substantially unaflected. Separation-of the tin, which may be in the form of tin oxide or tin hydrate, from the lead nitrate solution is 40' effected by decantation; it is then washed repeatedly with water and the washings are again decanted.

Each of the decantation operations involved in the above process may be carried out more 45 quickly and more emciently by proceeding in ac- Only a very small quantity of the emulsion need be employed in proceeding according to the ingo vention. For example, in separating lead carbonate or'tin oxide from aqueous suspension in accordance-with the above example, only that amount or emulsion corresponding to about four pounds of flour per twenty-five tons of pulp being treated was required to accomplish quick and thorough settlement of the solid matter. In the treatment of pulps containing other solids than those of the example, more or less than this Caustic soda with the present invention. In each amount of the emulsion may be required to secure the bestresults;

I claim:

1. In decanting a chemical or metallurgical soda to the mixture in an amount corresponding to one part of caustic soda to about 5 to parts of flour, and incorporating the resulting cooked emulsion in the pulp.

3. The method of increasing the rate of settlement of suspended matter in a chemicalor metallurgical pulp which comprises preparing a cooked emulsion comprising a starch-bearing material and an alkaline reagent by heating a mixture of the starch-bearing material, the alkaline reagent and water to a temperature sufiiciently high to effect emulsification of the starch-bearing material, and incorporating the resulting cooked emulsion in the pulp.

4. The method of increasing the rate of settlement of suspended matter in a chemical or metallurgical pulp which comprises preparing-a. cooked emulsion comprising a starch-bearing material and'an alkali metal compound by heating a mixture of the starch-bearing material, the 'alkali metal compound, and water substantially to the boiling point, and incorporating the resulting cooked emulsion in-the pulp.

5. The method of increasing the rate of settlement of lead carbonate from an aqueous pulp containing lead carbonate in suspension which comprises preparing a cooked aqueous emulsion by heating a mixture of flour, caustic soda and water substantially to the boiling point, adding the thus prepared emulsion to the pulp, and agitating the pulp to incorporate the emulsion therein.

6. In the processing of secondary metals involving the production of an aqueous pulp con-. taining a suspended tin compound and decantation of said pulp, the improvement which comprises preparing a cooked aqueous emulsion by heating a mixture of flour, caustic soda and water substantially to the boiling point, and incorporating the thus prepared emulsion in the pulp prior to decantation thereof, thereby to increase the rate of settlement of the tin compound.

7. The method of increasing the rate of settlement of suspended matter in a chemical or metallurgical pulp which comprises preparing a cooking emulsion comprising a starch-bearing material and an alkaline reagent by heating a mixture of the starch-bearing material, the alkaline regent and water substantially to the boiling point, and incorporating the resulting cooked emulsion in the pulp. 

